A recent outbreak of H5N9 bird flu in Merced, California, has raised concerns about the potential for two strains of avian influenza to spread among humans. The US has struggled to control the spread of H5N1, another strain that has been spreading among birds for years.
The H5N1 strain has already appeared in other animals and humans, with 67 reported cases, including one fatality in Louisiana. While there is no evidence of human-to-human transmission, the risk increases as the virus spreads.
In contrast, H5N9 has only recently started causing severe disease in birds, with nearly 119,000 birds killed in the recent outbreak. The US has not yet seen widespread spread of this strain.
However, mutations and genetic reassortments could change the pandemic potential of H5N9. Reassortment occurs when two or more viruses infect a single host and swap genetic material with each other. As more birds get infected, the likelihood of such events increases, making it essential to control the spread of bird flu among birds.
The failure to do so could put humans at risk. The US has struggled to contain H5N1, and now faces two strains of highly pathogenic avian influenza that could potentially spread among humans, leading to a pandemic.
Source: https://www.forbes.com/sites/brucelee/2025/01/30/first-reported-h5n9-bird-flu-outbreak-in-us-as-h5n1-keeps-spreading